The present invention relates generally to electric vehicles. More particularly, the present invention relates to the reduction of ignition-off draw current in electric vehicle main control modules.
Electric vehicle technology is under rapid development. The main focus of electric vehicle developmental programs is to produce cars that are competitive with present-day internal combustion engine vehicles. A significant motivation for using electronic vehicles is the current trend towards reducing emissions. Air pollution produced by internal combustion engine vehicles (ICEV""s) in large cities have reached significant levels. These levels can be dramatically decreased by active reduction of emissions from internal combustion engines. Studies have shown that considering only vehicle and power plant pollution, a significant switch to electric vehicles would practically eliminate carbon monoxide, ozone, and volatile organic compounds from the air. Thus, electric vehicles have a substantial relationship to the overall well being of today""s society as well as the viability of future generations.
For the electric vehicle to become a realistic option for transportation, the primary technological issue which must be improved upon is energy storage and use. Short range and long range charging times have daunted electric vehicle design efforts since the early 1990""s. A significant hindrance in this development has been related to ignition-off draw currents in electric vehicle control systems. Ignition-off draw currents are currents which are present when the vehicle ignition is in the xe2x80x9coffxe2x80x9d position. These currents place a substantial draw on auxiliary power which is an important component of electric vehicle energy storage systems. The main control module, which is responsible for monitoring and controlling major systems within the vehicle, is largely responsible for ignition-off draw (IOD) currents.
Specifically, a major reason for the IOD current phenomenon is the perceived need to continuously power the main control module (MCM) for monitoring activities even when the ignition is off. These activities include the performance of predetermined calculations and the detection of certain events. When the ignition is on, quantities like temperature, speed, current, and voltage are all relevant to sub-system operation. These quantities are measured with transducers that convert operating conditions into analog signals. The signals are then digitized and supplied to the MCM, which evaluates the sub-system signals and sends out various control signals. When the ignition is off, the MCM must also monitor the batteries, perform calculations on state-of-charge, and turn on the heaters to maintain battery temperature if required. The problem with present approaches is that they fail to realize that these calculations and functions do not have to continuously be made. Thus, while it is true that the MCM must occasionally be powered on, continuous operation is excessive and wasteful of resources. In other words, continuously powering the MCM when the ignition is in the off position results in unnecessarily high IOD currents.
More recent approaches have involved placing the MCM in a low-power mode. This approach, however, still requires the application of power to certain portions of the MCM and therefore fails to fully address the issue of IOD current. As already noted, high IOD currents deplete the auxiliary power which supplies such crucial functions as turning on the vehicle, power steering, power brake operation, headlight operation, and turn indicator control.
The present invention provides an electric vehicle low power supervisor controller for reducing ignition-off draw current in main control modules. The controller has a sleep controller for powering down the main control module until an interrupt event occurs. Interrupt events include activities such as placing the vehicle in charging mode and turning on the ignition. The sleep controller powers up the main control module when the interrupt event occurs. The supervisor controller also includes an interrupt monitor for determining when the interrupt event has occurred. A supervisor wait module establishes and controls an interrupt cycle, wherein the interrupt cycle is defined by an amount of time between determinations of the interrupt monitor. The supervisor wait module therefore places the main control module in a sleep mode during the interrupt cycle.
The present invention also provides a method for reducing ignition-off draw current in an electric vehicle with a low power supervisor controller. The method includes the steps of powering down a main control module until an interrupt event occurs, and determining when the interrupt event occurs. The method further includes the step of powering up the main control module when the interrupt event occurs. As an additional aspect, the method provides the step of placing the supervisor controller in a sleep mode when interrupt event determinations are not being made.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.